Health risk The UN has called for more research into the link between chemicals that disrupt hormones and diseases such as cancers and early breast development and poor semen quality.

Experts from the UN Environment Programme and World Health Organization say evidence is mounting that so-called 'endocrine disrupting chemicals' (EDCs) become a health risk when they enter the environment, but key knowledge gaps remain.

"However, only a small fraction of these chemicals have been investigated in tests capable of identifying overt endocrine effects in intact organisms."

The report was commissioned against a backdrop of concern that EDCs - found in some pesticides, electronics, personal care products, plastic additives, food additives and cosmetics - are entering water supplies and the food chain through agricultural run-off, waste dumps and other sources.

In recent decades, scientists have observed a rise in endocrine-related disorders in humans and wildlife, including studied populations of deer, sea lions and sea otters.

In some countries, up to 40 per cent of young men have low semen quality, which reduces their ability to father children, the report states.

"Global rates of endocrine-related cancers - breast, endometrial, ovarian, prostate, testicular and thyroid - have been increasing over the past 40 to 50 years," they say.

"There is a trend towards earlier onset of breast development in young girls in all countries where this has been studied. This is a risk factor for breast cancer."

Incidence of genital malformation in young boys, such as non-descending testes, has increased over time or levelled off "at unfavourably high rates", they add.

The UN experts say that the emergence of these disorders over such a short time rules out a genetic cause.

Laboratory studies back suspicions that EDCs are to blame, they say.

Knowledge gaps

But there are big gaps in knowledge, especially grass-roots studies that compare the incidence of these disorders and exposure to the chemicals, they say, adding there could be other environmental causes, while age and nutrition could also play a role.

In the quest for a fuller picture, the UN experts called for more research and better international co-ordination on testing standards and urged governments, in the meantime, to be vigilant.

"Worldwide, there has been a failure to adequately address the underlying environmental causes of trends in endocrine diseases and disorders," they say. "(The) disease risk due to EDCs may be significantly underestimated."